Process for producing chimeric cyclooligodepsipeptides in filamentous fungi

ABSTRACT

A method for obtaining at least one microbial secondary metabolite or a derivative thereof, the method includes the step of heterologous expression of at least one synthetase of the secondary metabolite in at least one filamentous fungus. Also disclosed is an expression cassette, a plasmid vector including the expression cassette, an expression host, novel cyclodepsipeptides and a chimeric cyclodepsipeptide synthetase.

The present invention relates to a method for obtaining microbial secondary metabolites according to claim 1, an expression cassette according to claim 16, a plasmid vector according to claim 17, cyclodepsipeptides according to claim 18, an expression host according to claim 19 and a chimeric cyclodepsipeptide synthetase according to claim 20.

DESCRIPTION

Recent genome mining efforts have uncovered that the genomes of filamentous fungi encode an unexpected rich repertoire of low molecular weight compounds with commercial relevance. These natural products known as secondary metabolites include nonribosomal peptides, polyketides and lipopeptides with pharmacological impact. However, most of the genes involved in secondary metabolism pathways are not expressed under standard laboratory or industrial conditions, what hampers application of these natural products. Different strategies based on molecular factors and cultivation methods have thus been undertaken. However, there are still major obstacles to overcome such as low production rates.

The present invention describes thus a novel approach for synthesizing microbial secondary metabolites or derivatives thereof, in particular cyclodepsipeptides.

The present method comprises the step of heterologous expression of at least one synthetase of said secondary metabolite in at least one filamentous fungus.

The filamentous fungi are preferably selected from the group of Aspergillus sp., Trichoderma sp., Penicillium sp., Fusarium sp. and Rhizopus spp. In particular preferred expression hosts are Aspergillus niger, Aspergillus oryzae, Aspergillus nidulans, Trichoderma reesei, Fusarium oxysporum, Rhizopus oryzae, Penicillium chrysogenum.

In an embodiment of the present method the synthetase is selected from the group of non-ribosomal peptide synthetase (NRPS), ribosomally synthesized and posttranslationally modified peptides (RiPPs), polyketide synthetase (PKS), terpene cyclases or hybrides thereof.

It is in particular preferred if the synthetase is a cyclodepsipeptidsynthetase, in particular a cyclodepsipeptidsynthetase of the iterative type. For example the synthetase is a cyclodepsipeptidsynthetase selected from the group containing Enniatin, PF1022, Beauvericin and Bassianolide synthetase.

It is in general also possible and conceivable to express further NRPS in one of the mentioned fungi, such as NRPS of epothilone, actinomycin, daptomycin, valinomycin, fungisporin or bleomycin.

In another variant it is desirable to express PKS systems, such as the one for erythromycin, doxycycline or geldanamycin in the fungal expression host.

The native cyclodepsipeptide synthetase typically comprises two modules: module 1 for integrating a D-hydroxycarboxylic acid, module 2 for integrating an L-amino acid and additionally a third PCP and C-domain (module 3) for determining the ring size n, typically n=6 and 8. A typical example of a cyclodepsipeptide synthetase, such as Enniatin Synthetase is shown in FIG. 1.

Enniatin is a hexacyclodepsipeptide consisting of 3 D-hydroxycarboxylic acids and 3 L-amino acids. Main products are Enniatin A, B, and C with Enniatin A comprising 3×D-Hiv, 3×L-Ile, Enniatin B comprising 3×D-Hiv, 3×L-Val and Enniatin C comprising 3×D-Hiv, 3×L-Leu. The N-atom is in any case methylated.

Enniatin is synthesized by a Enniatin Synthetase which is present in Fusarium sp., Vertcillium hemipterigenum, Halosarpheia sp. In case of Enniatin B module 1 is specific for D-hydroxyvalerate, module 2 is specific for L-valine and PCP/C-domain (module 3) determines the ring number n=6.

The PF1022 synthetase, which is for instant present in Mycelia sterilia, comprises module 1 specific for D-phenyllactate and/or D-lactate, module 2 specific for L-leucine and a PCP/C-domain (module 3) determining a ring number n=8.

The Beauvericin synthetase, for instance from Beauveria bassiana strain ATCC7159, comprise module 1 specific for D-hydroxyvalerate, module 2 specific for L-phenylalanine and PCP/C-domain (module 3) determining the ring number being n=6.

In another preferred embodiment a chimeric cyclodepsipeptide synthetase is used, wherein the synthetase is made of modules and/or domains of at least two different cyclodepsipeptide synthetases. It is preferred if at least one module is chosen from a first cyclodepsipeptide synthetase and and at least a second module is chosen from another cyclodepsipeptide synthetase. For example, it is possible that the synthetase comprises module 1 of one cyclodepsipeptide synthetase and modules 2 and 3 of another cyclodepsipeptide synthetase.

Preferred embodiments of such hybrid or chimeric cyclodepsipeptide synthetases can have the following arrangement:

-   -   a) module 1 from PF1022 Synthetase specific for         D-Phenyllactate/D-Lactate (for example from Mycelia sterilia),         module 2 and PCP/C-domain (module 3) from Enniatin Synthetase         specific for L-Valin and n=6 (for example from Fusarium         oxysporum; see FIG. 14, Seq ID No1), or     -   b) module 1 from PF1022 Synthetase specific for         D-Phenyllactate/D-Lactate, module 2 and PCP/C-domain (module 3)         from Beauvericin Synthetase specific for L-Phenylalanine and n=6         (see FIG. 18, Seq ID No 2).

In general any other module/domain combination is possible. For example it is conceivable and possible that module 1 is chosen from an Enniatin or Beauvericin Synthetase and module 2 and PCP/C-domain (module 3) are chosen from PF1022 Synthetase.

However, a hybrid cyclodepsipeptide synthetase system comprising module 1 from beauvericin synthetase and module 2 and PCP/C-domain (module 3) from bassianolide synthetase as the synthetase system, which has been shown to be expressed in Saccharomyces cerevisiae, is already known and is hereby exempted (Yu et al., ChemComm., 2013, 49:6176-6178). This specific chimeric cyclodepsipeptide synthetase is however not exempted from expression in a filamentous fungus.

In a further embodiment of the present invention an inducible expression system integrated into the chromosome of the at least one filamentous fungus is used for heterologous expression of at least one synthetase. Such an inducible expression system is independent on the metabolism. Also constitutive expression is in general possible.

In a variant the expression system comprises at least one expression cassette consisting of at least three modules. The expression cassette may comprise a first module for constitutive expression of the Tetracycline dependent transactivator rtTA2, a second module (Tet-on system) harboring the rtTA2-dependent promoter for inducible expression of the at least one secondary metabolite synthetase and a third module for integrating the cassette into the fungal genome by homologous recombination.

In a most preferred embodiment the first module comprises constitutive promoter PgpdA-rtTA-terminator TcgrA, the second module comprises operator sequence tetO7-(seven copies of tetO sequence)-minimal promoter Pmin-secondary metabolite synthase (esyn1)-terminator trpC (with tetO7::Pmin as rtTA2S-M2 dependent promoter) and the third module comprises pyrG* for homologous integration of the plasmid at the pyrG locus. After transformation of the plasmid vector comprising said expression cassette into a preferable protease-negative (prtT) and uracil-auxotroph (pyrG) A. niger strain, uridine-prototroph transformants were selected, purified and subjected to Southern analysis. The expression cassette is exemplarily shown in FIG. 2.

Other selection systems may be based on dominant (antibiotics such as hygromycin or phleomycin), auxotrophic or nutritional selection markers established for filamentous fungi.

At least one copy of the expression cassette is integrated into the fungal genome. It is possible that multiple expression cassettes are present in the fungal genome.

In another variant of the present invention the expression cassette comprises further genes encoding for biosynthetic enzymes of metabolic precursors or metabolic intermediates, in particular dehydrogenases. For example, using dehydrogenases for transforming amino acids to hydroxycarboxylic acids, which are expressed constitutively, allows an independent synthesis of different hydroxycarboxylic acids.

Said further genes may also not be part of the expression cassette and may be expressed from a different chromosomal location by using at least one constitutive, inducible or repressible promotor.

The transformed fungal expression host is grown in a suitable culture medium. The culture media used for heterologous expression of the synthetase may comprise talcum, titanic, silica or aluminium oxide particles, wherein talcum particles are in particular preferred. These particles support formation of smaller fungal pellets.

The culture media comprises furthermore glucose, trace elements, casamino acids, MgSO₄, yeast extracts. In one variant of the present method the glucose concentration is 1-10%, preferably 2.5 to 7.5%, mostly preferably 5%.

It is also preferred if the culture media used for heterologous expression of the synthetase comprises 5-50 mM, preferably 10-30 mM, most preferably 20 mM of at least one hydroxycarboxylic acid or derivatives thereof (for example 20 mM D-hydroxyvalerate) and 10-30 mM, preferably 15-25 mM, most preferably 20 mM of at least one amino acid or a derivative thereof (for example L-valine).

It is in general also possible to replace the hydroxycarboxylic acid by their corresponding esters, by O-acylated hydroxycarboxylc acids and their corresponding esters. The methyl esters are thereby preferred.

The induction of the expression occurs by adding the appropriate inducer, for example 5-200 μg/ml, in particular 10-100 μg/ml, most preferably 10-50 μg/ml doxycycline or other inducers such as tetracyclin or derivatives thereof. The addition of 10 μg/ml doxycycline is in particular preferred. The induction is preferably carried out in the exponential phase, in particular in batch or fed batch culture. The inducer can be added once or repeatedly.

In a further embodiment of the present invention the culture media used for heterologous expression of the synthetase comprises at least one D- or L-hydroxycarboxylic acid (or racemic mixtures thereof) of the general formulae (I) R¹—CHOH—CO₂H, wherein R¹ can be selected from a group comprising

-   -   substituted and non-substituted C₁-C₅₀-alkyl, substituted and         non-substituted C₂-C₅₀-alkenyl, substituted and non-substituted         C₂-C₅₀-alkinyl, substituted and non-substituted         C₃-C₁₀-cycloalkyl, substituted and non-substituted         C₅-C₇-cycloalkenyl, which in each case can be interrupted by one         or more oxygen atoms, sulphur atoms, substituted or         mono-substituted nitrogen atoms, double bonds and/or by one or         more groups of the type —C(O)O—, —IC(O)—, —C(O)—, —NHC(O)O—,         —CO(O)NH— and/or —OC(O)O—, or     -   aryl, heteroaryl, —CH₂-aryl or —CH₂-heteroaryl, wherein aryl and         heteroaryl are substituted or non-substituted.

Thus, the hydroxycarboxylic acids may be fed to the culture media during growth of the expression host. It is however also possible that at least some of the hydroxycarboxylic acids are synthesized by the expression host itself.

The moiety R¹ can be selected from a group comprising substituted and non-substituted C₁-C₁₂-alkyl, substituted and non-substituted C₃-C₇-cycloalkyl and substituted and non-substituted C₂-C₁₂-alkenyl and substituted and non-substituted C₆-C₁₂ Aryl, in particular —C₆H₅.

The term “substituted” in connection to alkyl, alkenyl, alkinyl, cycloalkenyl relates to the substitution of one or more atoms, usually H-atoms, by one or more of the following substituents: halogen, in particular F, Cl, Br, hydroxy, protected hydroxy, oxo, protected oxo, —N₃, C₃-C₇-cycloalkyl, phenyl, naphtyl, amino, protected amino, primary, secondary or tertiary amino, heterocyclic ring, imidazolyl, indolyl, pyrrolidinyl, C₁-C₁₂-alkoxy, C₁-C₁₂-acyl, C₁-C₁₂-acyloxy, nitro, carboxy, carbamoyl, carboxamid, N—(C₁-C₁₂-alkyl)carboxamid, N,N-Di(C₁-C₁₂-alkyl)carboxamid, cyano, methylsulfonylamino, thiol, C₁-C₁₀-alkylthio and C₁-C₁₀-alkylsulfonyl. The substituted groups can once or twice substituted with same or different substituents.

Examples for the above substituted alkyl groups comprise 2-oxo-prop-1-yl, 3-oxo-but-1-yl, cyanomethyl, nitromethyl, chlormethyl, hydroxymethyl, tetrahydropyranyloxymethy, trityloxymethyl, propionyloxymethyl, aminomethyl, carboxymethyl, allyloxycarbonylmethyl, allyloxycarbonylaminomethyl, methoxymethyl, ethoxymethyl, t-butoxymethyl, acetoxymethyl, chlormethyl, brommethyl, iodmethyl, trifluormethyl, 6-hydroxyhexyl, 2,4-dichlor(n-butyl), 2-aminopropyl, 1-chlorethyl, 2-chlorethyl, 1-bromethyl, 2-bromethyl, 1-fluorethyl, 2-fluorethyl, 1-iodethyl, 2-iodethyl, 1-chlorpropyl, 2-chlorpropyl, 3-chlorpropyl, 1-brompropyl, 2-brompropyl, 3-brompropyl, 1-fluorpropyl, 2-fluorptopyl, 3-fluorpropyl, 1-iodpropyl, 2-iodpropyl, 3-iodpropyl, 2-aminoethyl, 1-aminoethyl, N-benzoyl-2-aminoethyl, N-acetyl-2-aminoethyl, N-benzoyl-1-aminoethyl, N-acetyl-1-aminoethyl and alike.

Examples for the above substituted alkenylgroups comprise styrolyl, 3-chlor-propen-1-yl, 3-chlor-buten-1-yl, 3-methoxy-propen-2-yl, 3-phenyl-buten-2-yl, 1-cyano-buten-3-yl and alike.

The term “alkinyl” as used herein relates to a moiety of the formulae R—C≡C—, in particular to a C₂-C₅₀-Alkinyl”. Examples for C₂-C₅₀-alkinyle comprise ethinyl, propinyl, 2-butinyl, 2-pentinyl, 3-pentinyl, 2-hexinyl, 3-hexinyl, 4-hexinyl, 2-heptinyl, 3-heptinyl, 4-heptinyl, 5-heptinyl, octinyl, noninyl, decinyl, undecinyl, dodecinyl, as well as di- and tri-ines of straight or branched alky chains.

The term “oxo” relates to a carbon atom, which is connected with an oxygen atom via a double bond whereby a keto or an aldehyde group is formed. The term “protected oxo” relates to a carbon atom, which is substituted by two alkoxy groups or is connected twice with a substituted diol forming a non-cyclic or cyclic ketal group.

The term “alkoxy” relates to moieties like methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, t-butoxy and alike. A preferred alkoxy group is methoxy.

The term “C₃-C₇-cycloalkyl” comprises groups like cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl. The term “C₅-C₇-Cycloalkenyl” relates to a 1,2 oder 3-cyclopentenyl ring, a 1,2,3 oder 4-cyclohexenyl ring or a 1,2,3,4 or 5-cycloheptenylring.

Preferably R¹ is methyl, ethyl, —CH(CH₃)₂, propyl, isopropyl, —CH₂—CH(CH₃)₂, butyl, isobutyl, tert.-butyl, —CH₂—C(CH₃)₃, pentyl, hexyl, —CH₂—C₆H₅, —CH₂—Cl, —CH₂—Br, —CH₂—F, —CH₂—I, —CH₂—N₃, —CH₂—C≡CH, —CH₂CH═CH₂CH₃ or —CH₂-cycloC₃H₅.

In another preferred embodiment of the present invention the culture media used for heterologous expression of the synthetase comprises at least one D- or L-amino acid of the general formulae (II) R²—CHNH₂—CO₂H, wherein R² can be selected from the group comprising

-   -   substituted and non-substituted C₁-C₅₀-alkyl, substituted and         non-substituted C₂-C₅₀-alkenyl, substituted and non-substituted         C₂-C₅₀-alkinyl, substituted and non-substituted         C₃-C₁₀-cycloalkyl, substituted and non-substituted         C₅-C₇-cycloalkenyl, which in each case can be interrupted by one         or more oxygen atoms, sulphur atoms, substituted or         mono-substituted nitrogen atoms, double bonds and/or by one or         more groups of the type —C(O)O—, —OC(O)—, —C(O)—, —NHC(O)O—,         —OC(O)NH— and/or —OC(O)O—. In particular R² is —CH₂—C₆H₅         (phenyl), —CH₂—CH(CH₃)₂, —CH₂(CH₃)₂.

Thus, the amino acid may be fed to the culture media during growth of the expression host. The feeding of an amino acid to the culture media has only supportive character and improves the overall expression yield. It is however also possible (and common) that at least some of the amino acids, preferably the naturally occurring amino acids, are synthesized by the expression host itself.

Before transformation into the expression host the expression cassette is part of a plasmid vector.

An example for such a plasmid vector comprising an expression cassette with an Enniatin synthase is shown in FIG. 3. In this particular plasmid vector the Esyn gene (Enniatin synthetase) was cloned into Tet-On expression vector pVG2.2. Due to the large gene (9.4 kb) the cloning was performed by SLIC and homologous recombination method using pyrG as selection marker. However, other suitable cloning techniques are also applicable.

The integration process of the expression cassette into the chromosome of fungi, such as A. niger is exemplarily shown in FIG. 4. Integration into the genome can be by homologous or heterologous recombination thus resulting in transformants carrying either single- or multi-copy integrations of the expression cassette.

The present method allows for synthesizing at least one cyclodepsipeptide or a derivative thereof comprising the following general formulae (III)

wherein R¹ and R² have the above meanings, R³ is a C1-C3 alkyl moiety, in particular a —CH₃ moiety and m=3 or 4. Preferred Cyclodepsipeptides are shown in FIG. 10. In FIG. 11 the analytical data of Chloroenniatin obtained by feeding chlorolactate are shown.

Preferred variants are

-   Cyclo(-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-)     ([3 Cl-Lac]3 Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-lactyl-)     ([3 Cl-Lac]₂ [Lac]₁ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-D-lactyl-)     ([3 Cl-Lac]₁ [Lac]₂ Enniatin B) -   Cyclo(-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-)     ([3 Cl-Lac]₃ Enniatin B 2) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl)     ([3 Br-Lac]2 [Lac]1 Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-lactyl-)     ([3 Br-Lac]₂ [Lac]₁ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-D-lactyl-)     ([3 Br-Lac]₁ [Lac]₂ Enniatin B) -   Cyclo(-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-)     ([3 Br-Lac]₃ Enniatin B 2) -   Cyclo(-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-2-hydroxyisovaleryl-)     ([3 Br-Lac]₂ [D-Hiv]₁ Enniatin B) -   Cyclo(-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-2-hydroxy-lactyl-N-methyl-L-valyl-D-2-hydroxy-isovaleryl-)     ([3 Br-Lac]₁ [D-Hiv]₂ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-azidolactyl-N-methyl-L-valyl-D-3-azidolactyl-N-methyl-L-valyl-D-3-azidolactyl-)     ([3 N3-Lac]₃ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-azidolactyl-N-methyl-L-valyl-D-3-azidolactyl-N-methyl-L-valyl-D-lactyl-)     ([3 N3-Lac]₂ [Lac]₁ Enniatin) -   Cyclo(-N-methyl-L-valyl-D-3-fluorolactyl-N-methyl-L-valyl-D-3-fluorolactyl-N-methyl-L-valyl-D-3-fluorolactyl-)     ([3 F-Lac]₃ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-fluorolactyl-N-methyl-L-valyl-D-3-fluorolactyl-N-methyl-L-valyl-D-3-fluorolactyl-)     ([3 F-Lac]₂ [Lac]₁ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-iodolactyl-N-methyl-L-valyl-D-3-iodolactyl-N-methyl-L-valyl-D-3-iodolactyl-)     ([3 I-Lac]₃ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-iodolactyl-N-methyl-L-valyl-D-3-iodolactyl-N-methyl-L-valyl-D-lactyl-)     ([3 I-Lac]₂ [Lac]₁ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-iodolactyl-N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-D-lactyl-)     ([3 I-Lac]₁ [Lac]₂ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-cyclopropyllactyl-N-methyl-L-valyl-D-3-cyclopropyllactyl-N-methyl-L-valyl-D-3-cyclopropyllactyl-)     ([3 Cp-Lac]₃ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-chlorolactyl-)     ([3 Br-Lac]₁ [3 Cl Lac]₂ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-chlorolactyl-)     ([3 Br-Lac]₂ [3 Cl Lac]₁ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-propagyllactat-N-methyl-L-valyl-D-propagyllactat-N-methyl-L-valyl-D-propagyllactyl-)     ([3 Pr-Lac]₃ Enniatin B) -   Cyclo(-N-methyl-L-valyl-D-3-bromolactyl-N-methyl-L-valyl-D-3-chlorolactyl-N-methyl-L-valyl-D-3-lactyl-)     ([3 Br-Lac]₁ [3 Cl Lac]₁ [Lac]₁ Enniatin B) -   Cyclo(-L-valyl-d₆-D-2-hydroxy-isovaleryl-N-methyl-L-valyl-d₈-D-2-hydroxy-isovaleryl-N-methyl-L-valyl-d₆-D-2-hydroxy-isovaleryl-)     (d₁₈ Enniatin B) -   Cyclo     (—N-methyl-L-phenylalanyl-D-phenyllactyl-N-methyl-L-phenylalanyl-D-phenyllactyl-N-methyl-L-phenylalanyl-D-phenyllactyl-)     ([Phelac]₃ Beauvericin) -   Cyclo     (—N-methyl-L-valyl-D-phenyllactyl-N-methyl-L-valyl-D-phenyllactyl-N-methyl-L-valyl-D-phenyllactyl-)     ([Phelac]₃ Enniatin B) -   Cyclo     (—N-methyl-L-valyl-D-phenyllactyl-N-methyl-L-valyl-D-phenyllactyl-N-methyl-L-valyl-D-lactyl-)     ([Phelac]2 [Lac]₁ Enniatin B) -   Cyclo     (—N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-lactyl-)     ([Lac]₃ Enniatin B) -   Cyclo     (—N-methyl-L-D-valyl-D-phenylalanyl-N-methyl-L-valyl-D-lactyl-N-methyl-L-valyl-D-lactyl-)     ([Phelac]₁ [Lac]₂ Enniatin B) -   Cyclo     (—N-methyl-L-phenylalanyl-D-phenyllactyl-N-methyl-L-phenylalanyl-D-phenyllactyl-N-methyl-L-phenylalanyl-D-lactyl-)     ([Phelac]₂ [Lac]₁ Beauvericin)

The chemical structures of some of the above and further variants are shown below:

It is further possible and preferred to use the present method to produce isotopically labelled and/or in particular deuterated compounds which can be used as standards in analytical applications, for instance in mycotoxin analytics.

The invention is further explained by the following examples with reference to the Figures. It shows:

FIG. 1 a schematic view of the module arrangement of the cyclohexadepsipeptide synthetase (here enniatin synthetase);

FIG. 2 Schematic overview of the integrated and inducible expression system in filamentous fungi;

FIG. 3 Vector map of the expression plasmid with enniatin synthetase;

FIG. 4 Overview of single and multiple integration events in the pyrG locus;

FIG. 5 1H-NMR spectra of enniatin B obtained by heterologous expression of the corresponding synthase in A. niger;

FIG. 6 MS-spectra of enniatin B obtained by heterologous expression of the corresponding synthase in A. niger;

FIG. 7 MS/MS-spectra of enniatin B obtained by heterologous expression of the corresponding synthase in A. niger;

FIG. 8 13C-NMR spectra of enniatin B obtained by heterologous expression of the corresponding synthase in A. niger;

FIG. 9 X-Ray crystal structure of enniatin B;

FIG. 10 preferred enniatin derivatives;

FIG. 11 Analytical data of chloroenniatin;

FIG. 11a Analytical data for Beauvericin obtained from A. niger;

FIG. 12 Strategy for swapping whole modules between two fungal NRPS encoding sequences;

FIG. 13 Selected homologous region for swapping of hydroxy carboxylic acid activating module between PF1022- and enniatin/beauvericin synthetase;

FIG. 14 Overview of generating hybrid fungal NRPS: Sketch of a hybrid PFSYN/ESYN containing module 1 from PFSYN and module 2 from ESYN. The hydroxy carboxylic acid specificity comes from PF1022 (D-PheLac/D-Lac) the amino acid specificity from ESYN (L-Leu) to generate new cyclohexadepsipeptides;

FIG. 15 HPLC-ESI-MS of chimeric [PheLac]₀₋₃-enniatin derivatives. Solvent A: water with 0.1% HCOOH, solvent B: acetonitrile with ACN mit 0.1% HCOOH. Flow rate: 0.2 mL/min. Measurements were performed with ESI-Orbitrap-MS, Exactive, Thermo Fisher Scientific, HPLC 1200 Series (Agilent Technologies) and a gradient from 5% to 100% from 1 to 8 min and subsequently 100% B for 5 more minutes. Column: Grace Grom-Sil 120 ODS-4 HE, 2×50 mm, 3 μm. TCC=20° C.;

FIG. 16 Determination of identity of chimeric [PheLac]₀₋₃-enniatin cyclodepsipeptides by tandem MS measurements. m/z of fragments (cleavage at peptide or ester bonds) corresponds to loss of one or several amino or hydroxy acids as indicated. Solvent A: water, solvent B: isopropanol. Flow rate: 0.4 mL/min. Agilent Technologies ESI-Triple-Quadrupol-MS, 6460 Series, UHPLC 1290 Infinity-Series (Agilent Technologies). Column: Agilent Poroshell 120 EC-C18 3.0×50 mm. TCC=45° C.

FIG. 17 Structure formula of [PheLac]₃-Enniatin and HR-ESI-Orbitrap MS for determination of the molecular formula;

FIG. 18 Changing hydroxy carboxylic acid specification from beauvericin (D-Hiv) into PF1022 (D-PheLac/D-Lac);

FIG. 19 HPLC-ESI-MS of chimeric [PheLac]₂₋₃-beauvericin derivatives. Solvent A: water with 0.1% HCOOH, solvent B: acetonitrile with ACN mit 0.1% HCOOH. Flow rate: 0.2 mL/min. Measurements were performed with ESI-Orbitrap-MS, Exactive, Thermo Fisher Scientific, HPLC 1200 Series (Agilent Technologies) and a gradient from 5% to 100% from 1 to 8 min and subsequently 100% B for 5 more minutes. Column: Grace Grom-Sil 120 ODS-4 HE, 2×50 mm, 3 μm. TCC=20° C.;

FIG. 20 Determination of identity of chimeric [PheLac]₂₋₃-beauvericin cyclodepsipeptides by tandem MS measurements. m/z of fragments (cleavage at peptide or ester bonds) corresponds to loss of one or several amino or hydroxy acids as indicated. Solvent A: water, solvent B: isopropanol. Flow rate: 0.4 mL/min. Agilent Technologies ESI-Triple-Quadrupol-MS, 6460 Series, UHPLC 1290 Infinity-Series (Agilent Technologies). Column: Agilent Poroshell 120 EC-C18 3.0×50 mm. TCC=45° C.;

FIG. 21 Extracted ion chromatogramm of d18 enniatin B obtained from the feeding dependent A. niger strain. This substance can be used as an internal standard for the determination of enniatin in crops. A deuterated standard has never been reported yet. The system allows the synthesis of deuterated enniatin variants as well as beauvericin variants.

FIG. 22 Total Ion Chromatogram of [3-Br-Lac]₁ [Lac]₂ Enniatin B and Tandem MS of [3-Br-Lac]₁ [Lac]₂ Enniatin B;

FIG. 23 Tandem MS of [3-F-Lac]₃ Enniatin B;

FIG. 24 Tandem MS [3-N₃-Lac]₃ enniatin B. The azido group allows 1,3 dipolar cyclo addition for further chemical modification of the enniatin variant; and

FIG. 25 Tandem MS of [3-I-Lac]₃ enniatin B obtained by precursor directed biosynthesis in A. niger. Iodine containing enniatin variants undergo Elimination and substitution reactions.

A. FILAMENTOUS FUNGI AS EXPRESSION HOST 1. Terms and Definitions

-   -   Host:         -   A filamentous fungus belonging to the genera Aspergillus,             Trichoderma, Penicillium, Fusarium, Rhizopus     -   Dependent Host:         -   A host that is able to synthesize cyclodepsipeptides only if             precursors (hydroxy acids) are added to the medium             (example: A. niger strain DS3.1)     -   Independent Host:         -   A host that is able to synthesize cyclodepsipeptides without             addition of the precursors (example: A. niger strain ÖV3.4)

2. Protocol: PEG-Mediated Transformation of A. niger

The esyn1 gene of F. oxysporum was integrated in plasmid pVG2.2 to give plasmid pDS4.2 (FIG. 3) which comprises all three components of the Tet-on system:PgpdA::rtTA2S-M2 for constitutive expression of the transactivator rtTA, tetO7::Pmin::esyn1, which mediates esyn1 expression in a Dox-dependent manner and the pyrG* cassette, necessary for selection and targeting of the system to the pyrG locus of A. niger.

The performed transformation of A. niger is based on the method described by Punt et al. The used recipient strains were protease-negative (prtT) and uracil-auxotroph (pyrG⁻). The used constructs carry a mutated pyrG gene (pyrG*), which allows the transformants to grow on medium lacking uridine only after uptake of the foreign DNA and after homologous recombination of pyrG* with a mutated pyrG gene version of A. niger (both mutations are at different locations). The enniatin synthetase was expressed under control of the Tet-On expression system.

3. Materials and Solutions

-   -   SMC: 1.33 M sorbitol         -   50 mM CaCl₂         -   20 mM MES Buffer         -   pH 5.8     -   TC: 50 mM CaCl₂         -   10 mM Tris/HCl         -   pH 7.5     -   STC: 1.33 M sorbitol in TC     -   PEG buffer: 7.5 g PEG-6000         -   TC up to 30 mL     -   ASP+N (50×): 350 mM KCl         -   550 mM KH₂PO₄         -   3.5 M NaNO₃         -   pH 5.5     -   Vishniac: 76 mM ZnSO4         -   178 mM H₃BO₃         -   25 mM MnCl₂         -   18 mM FeSO₄         -   7.1 mM CoCl₂         -   6.4 mM CuSO₄         -   6.2 mM NaMoO₄         -   174 mM EDTA     -   protoplastation solution: 250 mg lysing enzyme from Trichoderma         harzianum         -   (Sigma)         -   SMC up to 10 mL         -   pH 5.6     -   MM: 20 mL ASP+N (50×)         -   20 mL glucose (50%)         -   2 mL MgSO₄         -   1 mL Vishniac         -   H₂O to 1 L         -   (addition of 2% agar for solid medium)     -   CM: MM, supplemented with:         -   10 mL casamino acids (10%)         -   50 mL yeast extract (10%)         -   H₂O to 1 L         -   (addition of 2% agar for solid medium)     -   Tranformation plates: 325.19 g sucrose         -   20 mL ASP+N         -   2 mL MgSO₄         -   1 mL Vishniac         -   12 g agar     -   Top agar: 325.19 g sucrose         -   20 mL ASP+N         -   2 mL MgSO₄         -   1 mL Vishniac         -   6 g agar

4. Experimental Procedure

The recipient strains (e.g. MA169.4 or AB1.13) were cultured in 100 mL of CM (+10 mM uridine) at 30° C. and 120 rpm for 10-16 h. The mycelium was collected over a myracloth filter and washed once with SMC. Afterwards, the collected mycelium was added to the protoplastation solution (in 50 mL test tube) and incubated for 1-1.5 h at 37° C. and 80 rpm. The protoplastation was confirmed by microscopy. Then, the protoplasts were collected through a myracloth filter and washed once with STC. The suspension was centrifuged for 10 min at 10° C. and 2000 rpm. The supernatant was decanted and the pellet gently resuspended in 1 mL of STC. The suspension was transferred to an Eppendorf tube and centrifuged for 5 min at 10° C. and 6000 rpm. Again, the supernatant was decanted and the protoplasts resuspended in 1 mL of STC. The wash step was repeated twice. For each transformation, 100 μL of protoplasts, 10 μg plasmid pDS4.2 (in 10 μL H₂O) and 25 μL PEG buffer were added to a 50 mL test tube and mixed gently. 1 mL of PEG buffer was added and the tube mixed gently. After 5 min, 2 mL STC were added and mixed. 20-25 mL of top agar (cooled to 40° C.) were added to the mixture and poured onto the prepared transformation plates (Ø 15 cm). The plates were incubated at 30° C. for 3-4 days. Afterwards, the transformants were purified twice by streaking the spores on MM plates for colony isolation. The purified strains were analyzed by PCR and Southern Blot to confirm proper uptake and insertion of plasmid pDS4.2 into the genome of the recipient strains (see FIG. 3).

5. Analytical Data for the Dependent Host Mutant DS3.1 Synthesizing Enniatin and Chloroenniatin (FIGS. 9 5 to 11)

Cultivation Conditions:

In order to identify the optimum condition for high yield production of enniatin a design-of-experiment approach was followed using the statistical software program MODE. The following parameters were varied in shake flask cultures of esyn1-expressing strain DS3.1: medium composition (minimal medium, complete medium, Fusarium defined medium), amino acid (in particular L-valine, L-leucine, L-isoleucine) supplementation (0-20 mM), hydroxyacid (in particular D-Hiv) supplementation, 0-50 mM), glucose concentration (1-5%), temperature, cultivation time (1-92 h) and Dox-concentration (0-20 μg/ml). The parameters which mainly affected the enniatin yields were Dox and D-Hiv. The best cultivation medium identified contained 20 mM D-Hiv, 20 mM of one of the amino acids and 10 μg/ml Dox. This medium composition improved the enniatin yield by a factor of 200. The enniatin yield was further increased about 4.75 fold by increasing the glucose concentration to 5% and by adding talcum.

-   -   Enniatin Production Medium (EM): 20 mL ASP+N (50×)         -   100 mL glucose (50%)         -   2 mL MgSO₄         -   1 mL Vishniac         -   10 mL casamino acids (10%)         -   50 mL yeast extract (10%)         -   100 mL talc (10% in 50 mM Na-acetate buffer, pH 6.5)         -   H₂O to 1 L

Strain DS3.1 (inoculation with 5×10⁶ spores/mL) was cultivated in EM at 26° C. and 250 rpm. After 16 h, 10 mM or 20 mM D-Hiv, 20 mM I-Val and 10 μg/mL Dox were added. The biomass was harvested after 92 h, lyophilized and enniatin B extracted with ethyl acetate.

Analytical Methods (See FIGS. 5-9, 11):

¹H-NMR and ¹³C-NMR spectra of enniatin B were recorded on a Bruker Avance 400 NMR-spectrometer. Chemical shifts are given in δ-units (ppm) relative to the solvent signal. IR spectra were recorded on a Jasco FT-IR 4100 spectrometer. HRMS using ESI-technique was performed on a LTQ Orbitrap XL apparatus. The enniatin samples were directly infused into the mass spectrometer.

Data for single-crystal structure determination of enniatin B were collected on an Oxford-Diffraction Xcalibur diffractometer, equipped with a CCD area detector Sapphire S and a graphite monochromator utilizing MoK_(α) radiation (λ=0.71073 Å). Suitable crystals were attached to glass fibers using fluoropolyalkylether oil (ABCR) and transferred to a goniostat where they were cooled to 150 K for data collection. Software packages used: CrysAlis CCD for data collection, CrysAlis Pro for cell refinement and data reduction.

Results:

Enniatin B:

A production of enniatin B up to 1000 mg/L in strain DS3.1 could be obtained and verified by MRM-analysis.

393 mg of purified enniatin B could be isolated from the biomass (27.5 mg) and the broth of a 1-L cultivation of transformant DS3.1 with supplementation of 10 mM d-Hiv and 20 mM I-Val to the medium.

The isolated enniatin B was analyzed my MS, MS/MS, IR, NMR and X-Ray crystallography (see FIGS. 5-10):

¹H-NMR (400.1 MHz, CDCl₃) δ=5.11 (d, ³J_(H,H)=8.7 Hz, 3H), 4.49 (d, ³J_(H,H)=9.7 Hz, 3H), 3.11 (s, 9H), 2.32-2.21 (m, 6H), 1.05-0.86 ppm (m, 36H); ¹³C-NMR (100.6 MHz, CDCl₃) δ=170.25, 169.31, 75.67, 63.20, 33.26, 29.91, 27.92, 20.42, 19.34, 18.72, 18.50 ppm; IR (Neat): v=2963.6-2873.4 (C—H, CH₃ and CH), 1736.1 (C═O, ester), 1660.9 (C═O, amide), 1183.6 (C—H, isopropyl) 1011.0 (CO, α-hydroxycarboxylic acid); ESI-HRMS: m/z calcd for [C₃₃H₅₇N₃O₉+Na]⁺: 662.39870; found: 662.39859.

Generation of Enniatin Analogs:

Protocol for Feeding Experiments:

Strain DS3.1 was cultivated under the same conditions as described above. Instead of D-Hiv, the corresponding hydroxy acid chlorolactate were added (10 mM final concentration). Feeding can be performed once or repeatedly at different time intervals during batch or fed batch cultivation.

An equivalent approach provided Beauvericin (see FIG. 11a ).

B) METHODS AND ANALYTICAL DATA FOR GENERATION OF HYBRID SYNTHETASE 1. Cloning Strategy for Generating Chimeric Synthetases (See FIGS. 12-14, 18)

Expression plasmids using T7 promoter for heterologous expression in E. coli were purchased from Merck Millipore. Protein expression of all hybrid genes coding for NRPS were cloned by insertion via restrictions sites into the high copy pRSF-Duet1 plasmid. Combinatorial biosynthesis was performed by λ-recombination mediated system. Sequences of desired domain or module were amplified via PCR (Q5-polymerase, High-Fidelity, New England Biolabs) and sub cloned into pRSF-Duet1. A selection marker (coding sequence for streptomycin resistance) which is needed after recombination was integrated at a single restriction site into the subcloned fragment. Positive clones were screened for streptomycin resistance and subsequently removed resistance by restriction and self-ligation of the flanking single cutter site. Electro competent E. coli BW25113 cells were transformed with the desired vector with the original NRPS gene cultivated at 30° C. to save the heat labile plasmid pIJ790 harbouring λ-recombinase RED (gam, bet, exo) and single DNA protecting proteins. Recombinase expression was induced by addition of arabinose before E. coli BW25113 cells were transformed with the module containing plasmid up to 70 base pairs were chosen as overlapping homologous region (modified after Gust et al./Zhang et al. 1998).

2. Production of Chimeric Enniatins and Beauvericins with Chimeric Synthetases Expressed in E. coli

Culture Conditions and Extraction

E. coli BI21gold cells were pre cultured over night at 37° C. in 20 ml of LB-medium at 200 rpm. Inoculation of main culture (50 ml LB-medium) with pre culture in the ration 1:100 was incubated to an OD₆₀₀ of 0.6 at 37° C. and induced with IPTG at a final concentration of 0.25 mM (Carl Roth) and further incubated for protein expression and peptide production at 18° C. for 24-48 h 200 rpm. Cells were harvested and cell pellet was extracted with 5 ml of MeOH (technical grade). The suspension was sonified for 5 minutes and supernatant was evaporated.

Analysis with HPLC-ESI-MS, HPLC-ESI-MS and Tandem MS (See FIGS. 15-17, 19-25)

For complex analytics crude extracts were resolved in 200-500 μl MeOH (HPLC grade) and suspended solids were centrifuged at 14 000×g. HPLC-ESI-MS was carried out for scanning new derivatives. For all measurements we used Agilent technologies regarding columns and HPLC/MS equipment (Eclipse Plus C18, 2.1×50 mm; UHPLC 1290 Infinity-Series, ESI-Triple-Quadrupol-MS, 6460 Series). By using a mobile phase system we added of 0.1% of HCOOH in H₂O (A) and ACN (B) with a gradient from 5% to 100% over 2.5 min and subsequently 100% B for 5.5 more minutes. 

1. Method for obtaining at least one microbial secondary metabolite or a derivative thereof, or isotopically labeled one, the method comprising the step of heterologous expression of at least one synthetase of said secondary metabolite in at least one filamentous fungus.
 2. Method according to claim 1 characterized in that the filamentous fungus is selected from the group of Aspergillus sp., Trichoderma sp., Penicillium sp., Fusarium sp. and Rhizopus sp.
 3. Method according to claim 1 or 2, characterized in that the synthetase is selected from the group of non-ribosomal peptide synthetases (NRPS), polyketide synthetases (PKS), ribosomally synthesized peptides and posttranslationally modified peptides (RiPPs), terpene cyclases or hybrides thereof.
 4. Method according to one of the preceding claims, characterized in that the synthetase is a cyclodepsipeptide synthetase, in particular a cyclodepsipeptide synthetase of the iterative type.
 5. Method according to one of the preceding claims, characterized in that the synthetase is a cyclodepsipeptide synthetase selected from the group containing Enniatin, PF1022, Beauvericin and Bassianolide synthetase.
 6. Method according to one of the preceding claims characterized in that the synthetase comprises modules and/or domains of at least two different cyclodepsipeptide synthetases.
 7. Method according to claim 6, characterized in that the synthetase comprises module 1 of one cyclodepsipeptide synthetase and module 2 or and PCP/C-domain of another cyclodepsipeptide synthetase.
 8. Method according to one of the preceding claims characterized in that an inducible expression system integrated into the chromosome of the at least one filamentous fungus is used for heterologous expression of the at least one synthetase.
 9. Method according to claim 8, characterized in that the expression system comprises at least one expression cassettes consisting of at least three modules.
 10. Method according to claim 9, characterized in that the expression cassette comprises a first module for constitutive expression of the tetracycline dependent transactivator rtTA2, a second module harboring the rtTA2-dependent promoter for inducible expression of the at least one secondary metabolite synthetase and a third module for integrating of the cassette into the fungal genome by homologous or heterologous recombination using appropriate selection markers.
 11. Method according to one of the claim 9 or 10, characterized in that the expression cassette comprises further genes encoding for biosynthetic enzymes of metabolic precursors or metabolic intermediates, in particular dehydrogenases.
 12. Method according to one of the preceding claims characterized in that the culture media used for heterologous expression of the synthetase comprises talc, titanic, silica or aluminium oxide particles.
 13. Method according to one of the preceding claims characterized in that the culture media used for heterologous expression of the synthetase comprises 5-20 mM, preferably 5-15 mM, most preferably 10 mM of at least one hydroxycarboxylic acid or derivatives thereof and 10-30 mM, preferably 15-25 mM, most preferably 20 mM of at least one amino acid or derivatives thereof.
 14. Method according to one of the preceding claims that the culture media used for heterologous expression of the synthetase comprises at least one D- or L-hydroxycarboxylic acid of the general formulae R¹—CHOH—CO₂H, wherein R¹ can be selected from a group comprising substituted and non-substituted C₁-C₅₀-alkyl, substituted and non-substituted C₂-C₅₀-alkenyl, substituted and non-substituted C₂-C₅₀-alkinyl, substituted and non-substituted C₃-C₁₀-cycloalkyl, substituted and non-substituted C₅-C₇-cycloalkenyl, which in each case can be interrupted by one or more oxygen atoms, sulphur atoms, substituted or mono-substituted nitrogen atoms, double bonds and/or by one or more groups of the type —C(O)O—, —OC(O)—, —C(O)—, —NHC(O)O—, —OC(O)NH— and/or —OC(O)O— aryl, heteroaryl, —CH₂-aryl or —CH₂-heteroaryl, wherein aryl and heteroaryl are substituted or non-substituted.
 15. Method according to one of the preceding claims, characterized in that the culture media used for heterologous expression of the synthetase comprises at least one D- or L-amino acid of the general formulae R²—CHNH₂—CO₂H, wherein R² can be selected from the group comprising substituted and non-substituted C₁-C₅₀-alkyl, substituted and non-substituted C₂-C₅₀-alkenyl, substituted and non-substituted C₂-C₅₀-alkinyl, substituted and non-substituted C₃-C₁₀-cycloalkyl, substituted and non-substituted C₅-C₇-cycloalkenyl, which in each case can be interrupted by one or more oxygen atoms, sulphur atoms, substituted or mono-substituted nitrogen atoms, double bonds and/or by one or more groups of the type —C(O)O—, —OC(O)—, —C(O)—, —NHC(O)O—, —OC(O)NH— and/or —OC(O)O—.
 16. Expression cassette according to one of the claims 9 to
 11. 17. Plasmid vector comprising at least one expression cassette according to claim
 16. 18. Cyclodepsipeptide or a derivative thereof obtainable by a method according to one of the claims comprising the following general formulae (III)

wherein R¹ and R² have the above meanings, R³ is a C1-C3 alkyl moiety, in particular a —CH₃ moiety and m=3 or
 4. 19. Expression host in form of a filamentous fungi comprising at least one expression cassette according to one of the claims 9 to 11 and
 16. 20. Chimeric cyclodepsipeptide synthetase, wherein the synthetase is made of modules/domains of at least two different cyclodepsipeptide synthetases.
 21. Chimeric cyclodepsipeptide synthetase according to claim 20, characterized in that, at least one module and/or domain is chosen from a first cyclodepsipeptide synthetase and and at least a second module is chosen from another cyclodepsipeptide synthetase. 